Ultracold Electrons via Near-Threshold Photoemission from Single-Crystal Cu(100)

Siddharth Karkare, Gowri Adhikari, W. Andreas Schroeder, J. Kevin Nangoi, Tomas Arias, Jared Maxson, Howard Padmore

Research output: Contribution to journalArticlepeer-review

35 Scopus citations


Achieving a low mean transverse energy or temperature of electrons emitted from the photocathode-based electron sources is critical to the development of next-generation and compact X-ray free electron lasers and ultrafast electron diffraction, spectroscopy, and microscopy experiments. In this Letter, we demonstrate a record low mean transverse energy of 5 meV from the cryo-cooled (100) surface of copper using near-threshold photoemission. Further, we also show that the electron energy spread obtained from such a surface is less than 11.5 meV, making it the smallest energy spread electron source known to date: More than an order of magnitude smaller than any existing photoemission, field emission, or thermionic emission based electron source. Our measurements also shed light on the physics of electron emission and show how the energy spread at few meV scale energies is limited by both the temperature and the vacuum density of states.

Original languageEnglish (US)
Article number054801
JournalPhysical Review Letters
Issue number5
StatePublished - Jul 31 2020

ASJC Scopus subject areas

  • General Physics and Astronomy


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